2.1 Pathobiology of MPD
Myeloproliferative disease (MPD) refers to a group of disorders characterized by clonal abnormalities of the hematopoietic stem cell. See e.g., Current Medical Diagnosis & Treatment, pp. 499 (37th ed., Tierney et al. ed, Appleton & Lange, 1998). Since the stem cell gives rise to myeloid, erythroid, and platelet cells, qualitative and quantitative changes can be seen in all these cell lines. Id.
MPD is further subdivided on the basis of the predominantly proliferating myeloid cell type. Erythrocyte excess is classified as “polycythemia rubra vera (PRV)” or “polycythemia vera,” platelet excess as “primary (or essential) thromobocythemia (PT),” and granulocyte excess as “chronic myelogenous leukemia (CML).” A fourth subcategory of MPD is “agnogenic myeloid metaplasia (AMM),” which is characterized by bone marrow fibrosis and extramedullary hematopoiesis. Cecil Textbook of Medicine, pp. 922 (20th ed., Bennett and Plum ed., W.B. Saunders Company, 1996). These disorders are grouped together because the disease may evolve from one form into another and because hybrid disorders are commonly seen. Tierney et al, supra, at pp. 499. All of the myeloproliferative disorders may progress to acute leukemia naturally or as a consequence of mutagenic treatment. Id.
Most patients with PRV present symptoms related to expanded blood volume and increased blood viscosity. Id. at pp. 500. Common complaints include headache, dizziness, tinnitus, blurred vision, and fatigue. Id. The spleen is palpably enlarged in 75% of cases, but splenomegaly is nearly always present when imaged. Id. Thrombosis is the most common complication of PRV and the major cause of morbidity and death in this disorder. Thrombosis appears to be related to increased blood viscosity and abnormal platelet function. Id. Sixty percent of patients with PRV are male, and the median age at presentation is 60. It rarely occurs in adults under age 40. Id.
Thrombosis is also a common complication in patients suffering from PT. Cecil Textbook of Medicine, pp. 922 (20th ed., Bennett and Plum ed., W.B. Saunders Company, 1996). A platelet count ≦6×105 per microliter has been set to diagnose PT. Tefferi et al., Mayo Clin Proc 69:651 (1994). Most patients are asymptomatic when PT is diagnosed, usually through incidental discovery of increased peripheral blood platelet count. Bennett and Plum, supra, at pp. 922. Approximately one quarter, however, have either thrombotic or hemorrhagic events. Id. PT rarely transforms into acute leukemia or AMM, and most patients have a normal life expectancy. Id. at pp. 923. However, at least one third of patients with PT eventually undergo major thrombohemorrhage complications. Id.
AMM is characterized by fibrosis of the bone marrow, splenomegaly, and a leukoerythroblastic peripheral blood picture with teardrop poikilocytosis. Id. at pp. 502. AMM develops in adults over age 50 and is usually insidious in onset. Id. Later in the course of the disease, bone marrow failure takes place as the marrow becomes progressively more fibrotic. Id. Anemia becomes severe. Id. Painful episodes of splenic infarction may occur. Severe bone pain and liver failure also occur in the late stage of AMM. Id. The median survival from time of diagnosis is approximately 5 years. Id. at pp. 503.
The precise cause of MPD is not clear. Current data suggest some growth factors are involved. For instance, in both PRV and PT, in contrast to normal erythroid progenitor cells, polycythemia vera erythroid progenitor cells can grow in vitro in the absence of erythropoietin due to hypersensitivity to insulin like growth factor I. Harrison's Principles of Internal Medicine, pp. 701 (15th ed., Braunwald et al. ed., McGraw-Hill, 2001). In AMM, the overproduction of type III collagen has been attributed to platelet-derived growth factor or transforming growth factor β (TGF-β). Id. at pp. 703; see also, Martyr, Leuk Lymphoma 6:1 (1991).
In some MPD forms, specific chromosomal changes are seen. For instance, nonrandom chromosome abnormalities, such as 20q-, trisomy 8 or 9 have been documented in a small percentage of untreated PRV patients, and 20q-, 13q-, trisomy Iq are common in AMM patient. Harrison's Principles of Internal Medicine, pp. 701-3 (15th ed., Braunwald et al. ed., McGraw-Hill, 2001). Philadelphia chromosome is present in the bone marrow cells of more than 90% of patients with typical CML and some patients with PRV. See e.g., Kurzrock et al., N Engl J Med 319:990 (1988). The Philadelphia chromosome results from a balanced translocation of material between the long arms of chromosomes 9 and 22. The break, which occurs at band q34 of the long arm of chromosome 9, allows translocation of the cellular oncogene C-ABL to a position on chromosome 22 called the brcakpoint cluster region (bcr). The apposition of these two genetic sequences produces a new hybrid gene (BCR/ABL), which codes for a novel protein of molecular weight 210,000 kD (P210). The P210 protein, a tyrosine kinase, may play a role in triggering the uncontrolled proliferation of CML cells. See e.g., Daley et al., Science 247:824 (1990).
The incidence of MPD varies depending on the form of the disease. PRV is diagnosed in 5-17 persons per 1,000,000 per year. Cecil Textbook of Medicine, pp. 920-926 (20th ed., Bennett and Plum ed., W.B. Saunders Company, 1996). True incidences of PT and AMM are not known because epidemiological studies on these disorders are inadequate. Id. Internationally, PRV is reportedly lower in Japan, i.e., 2 person per 1,000,000 per year. Id.
2.2 MPD Treatment
The treatment of choice for PRV is phlebotomy. Current Medical Diagnosis & Treatment, pp. 501 (37th ed., Tiemey et al. ed, Appleton & Lange, 1998). One unit of blood (approximately 500 mL) is removed weekly until the hematocrit is less than 45%. Id. Because repeated phlebotomy produces iron deficiency, the requirement for phlebotomy has to be gradually decreased. Id. It is important to avoid medicinal iron supplementation, as this can thwart the goals of a phlebotomy program. Id.
In more severe cases of PRV, myelosuppressive therapy is used. Id. One of the widely used myelosuppressive agents is hydroxyurea. Id. Hydroxyurea is an oral agent that inhibits ribonucleotide reductase. Bennett and Plum, supra, at pp. 924. The usual dose is 500-1500 mg/d orally, adjusted to keep platelets <500,000/μL without reducing the neurophil count to <2000/μL. Tierney et al, supra, at pp. 501. Side effects of hydroxyurea include mild gastrointestinal complaints, reversible neutropenia, and mucocutaneous lesions. Bennett and Plum, supra, at pp. 924. Busulfan may also be used in a dose of 4-6 mg/d for 4-8 weeks. Tierney et al., supra, at pp. 501. Alpha interferon has been shown to have some ability to control the disease. The usual dose is 2-5 million units subcutaneously three times weekly. Id. Anagrelide has also been approved for use in treatment of thrombocytosis. Id. Some of the myelosuppressive agents, such as alkylating agents and radiophosphorus (32P), have been shown to increase the risk of conversion of PRV to acute leukemia. Id. Using myelosuppressive agents for long period may cause prolonged severe myclosuppression.
Most authorities agree that treatment of PT should be aimed at decreasing the level of platelets in patients with a history of thrombosis as well as those with cardiovascular risk factors. Bennett and Plum, supra, at pp. 923. However, the benefit of specific therapy has not been established, and there is concern about the leukemogenic potential of the available therapeutic agents. Id. When treatment is decided upon, the initial drugs are hydroxyurea or anagrelide. Id. at pp. 924. Anagrelide is an oral agent that may involve inhibition of megakaryocyte maturation. Id. The starting dose is 0.5 mg given four times a day. Id. It is relatively contraindicated in elderly patients with heart disease. Id. Alpha interferon can also be used in the treatment of PT. Id.
Currently, there is no specific treatment for AMM. Tierney et al., supra, at pp. 502. The management of AMM is directed to symptoms. Anemic patients are supported with red blood cells in transfusion. Id. Androgens such as oxymetholone, 200 mg orally daily, or testosterone help reduce the transfusion requirement in one third of cases but are poorly tolerated by women. Id. Splenectomy is indicated for splenic enlargement that causes recurrent painful episodes, severe thrombocytopenia, or an unacceptable high red blood cell transfusion requirement. Id. Alpha interferon (2-5 million units subcutaneously three times weekly) leads to improvement in some cases. Id.
Since most therapies used in the treatment of MPD are targeted only at symptoms, and most agents used have serious side effects, with the danger of causing severe myclosuppression or converting the disorder to acute leukemia, there is a great need to find new treatments of MPD that either target the underlying cause of the disorder or improve the effectiveness and safety of the current treatments.
2.3 Thalidomide and Other Compounds Useful in the Treatment of Disease
Thalidomide is a racemic compound sold under the tradename Thalomid® and chemically named α-(N-phthalimido)glutarimide or 2-(2,6-dioxo-3-piperidinyl)-1H-isoindole-1,3(2H)-dione. Thalidomide was originally developed in the 1950's to treat morning sickness, but due to its teratogenic effects was withdrawn from use. Thalidomide has been approved in the United States for the acute treatment of the cutaneous manifestations of erythema nodosum leprosum in leprosy. Physicians' Desk Reference, 1154-1158 (56th ed., 2002). Because its administration to pregnant women can cause birth defects, the sale of thalidomide is strictly controlled. Id. Thalidomide has reportedly been studied in the treatment of other diseases, such as chronic graft-vs-host disease, rheumatoid arthritis, sarcoidosis, several inflammatory skin diseases, and inflammatory bowel disease. See generally, Koch, H. P., Prog. Med. Chem. 22:165-242 (1985). See also, Moller, D. R., et al., J. Immunol. 159:5157-5161 (1997); Vasiliauskas, E. A., et al., Gastroenterology 117:1278-1287 (1999); Ehrenpreis, E. D., et al., Gastroenterology 117:1271-1277 (1999). It has further been alleged that thalidomide can be combined with other drugs to treat ischemia/repercussion associated with coronary and cerebral occlusion. See U.S. Pat. No. 5,643,915, which is incorporated herein by reference.
More recently, thalidomide was found to exert immunomodulatory and anti-inflammatory effects in a variety of disease states, cachexia in AIDS, and opportunic infections in AIDS. In studies to define the physiological targets of thalidomide, the drug was found to have a wide variety of biological activities exclusive of its sedative effect including neurotoxicity, teratogenicity, suppression of TNF-α production by monocytes/macrophages and the accompanying inflammatory toxicities associated with high levels of TNF-α, and inhibition of angiogenesis and neovascularization.
Additionally, beneficial effects have been observed in a variety of dermatological conditions, ulcerative colitis, Crohn's disease, Bechets's syndrome, systemic lupus erythematosis, aphthous ulcers, and lupus. The anti-angiogenic properties of thalidomide in in vivo models have been reported. D'Amato et al., Thalidomide Is An Inhibitor Of Angiogenesis, 1994, PNAS, USA 91:4082-4085.
One of the most therapeutically significant potential uses of thalidomide is in the treatment of cancer. The compound has been investigated in the treatment of various types of cancer, such as refractory multiple myeloma, brain, breast, colon, and prostate cancer, melanoma, mesothelioma, and renal cell carcinoma. See, e.g., Singhal, S., et al., New England J. Med. 341(21):1565-1571 (1999); and Marx, G. M., et al., Proc. Am. Soc. Clin. Oncology 18:454a (1999). Thalidomide reportedly can also be used to prevent the development of chronic cardiomyopathy in rats caused by doxorubicin. Costa, P. T., et al., Blood 92(10: suppl. 1):235b (1998). Other reports concerning the use of thalidomide in the treatment of specific cancers include its combination with carboplatin in the treatment of glioblastoma multiforne. McCann, J., Drug Topics 41-42 (Jun. 21, 1999). The use of thalidomide in combination with dexamethasone reportedly was effective in the treatment of patients suffering from multiple myeloma who also received, as supportive care, human granulocyte colony-stimulating factor (G-CSF), ciprofloxacin, and non-absorbable antifungal agents. Kropff, M. H., Blood 96(11 part 1):168a (2000); see also, Munshi, N. et al., Blood 94(10 part 1):578a (1999). Other chemotherapy combinations that comprise thalidomide are disclosed in International Application No. PCT/US01/15326 to R. Govindarjan and A. Zeitlan, and in International Application No. PCT/US01/15327 to J. B. Zeldis, et al.
In an effort to provide compounds that have greater therapeutic safety and efficacy than thalidomide, researchers have begun investigating a large number of other compounds, some of which are derivatives of thalidomide. See, e.g., Marriott, J. B., et al., Expert Opin. Biol. Ther. 1(4):1-8 (2001); G. W. Muller, et al., Journal of Medicinal Chemistry 39(17):3238-3240 (1996); and G. W. Muller, et al., Bioorganic & Medicinal Chemistry Letters 8:2669-2674 (1998). Examples include, but are not limited to, the substituted 2-(2,6-dioxopiperidin-3-yl)phthalimies and substituted 2-(2,6-dioxopiperidin-3-yl)-1-oxoisoindoles described in U.S. Pat. Nos. 6,281,230 and 6,316,471, both to G. W. Muller, et al.
A group of compounds selected for their capacity to potently inhibit TNF-α production by LPS stimulated PBMC has been investigated. L. G. Corral, et al., Ann. Rheum. Dis. 58: (Suppl I) 1107-1113 (1999). These compounds, which are referred to as IMiDs™ or Immunomodulatory Drugs, show not only potent inhibition of TNF-α but also marked inhibition of LPS induced monocyte IL1β and IL12 production. LPS induced IL6 is also inhibited by IMiDs™, albeit partially. These compounds are potent stimulators of LPS induced IL10, increasing IL10 levels by 200 to 300%. Id.
While many such compounds have shown promise as therapeutic agents, their mechanisms of action and effectiveness are still under investigation. Moreover, there remains a need for therapeutic agents to treat MPD and its related disorders.